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<br />1 <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />selenium toxicity, etc., is primarily responsible for lack of spawning success, survival, and <br />recruitment. <br /> <br />The numbers desired for stocking are based on recovery goal criteria for fish population <br />abundance (USFWS 200lb) and survivorship curve estimates for razorback sucker provided in <br />Table 2. The target stocked population objective of 7,540 fish comprised of three age groups in <br />Table 2 is equal to the draft recovery goal abundance objective of 5,800 fish plus a 30% buffer <br />presuming natural adult mortality is 30% annually. If available, the 16,440 Age 2+ fish 2. 300 <br />mm in length would be stocked annually and would be split equally among the three river reaches <br />(Table 1). As. adults, these fish would constitute one presumptive genetic population as described <br />in Czapla (1999). A genetic risk assessment for broodstock development and stocking within this <br />plan is not necessary due to previous documentation. The appropriate genetic make-up for <br />broodstock has already been identified (Wydoski 1994), and the appropriate breeding strategy is <br />already being implemented within the Progranl at hatchery and pond facilities in Grand Junction, <br />Colorado, and Horsethief State Wildlife Area. Numbers of progeny from these broodstock family <br />lots that are in excess of those needed for production of the broodstock have already been <br />designated as suitable for stocking in the Colorado and Gunnison rivers (Czapla 1997). Burdick <br />et al. (1995) have already conducted a risk assessment associated with stocking and the stocking <br />plan has already been approved for implementation by the Recovery Progranl Biology Committee. <br /> <br />Achievement of the stocking objective would result in an adult population of at least 5,800 <br />adult fish from ages five to seven distributed over 150 river miles of three reaches in the Upper <br />Colorado River subbasin. <br /> <br />Stocking of razorback sucker will inteIject an additional species into the existing fish <br />community, and has the potential to induce changes in the relative abundance and biomass of these <br />species' populations in each of the targeted reaches. The stocking numbers proposed are <br />influenced by the following assumptions: <br /> <br />1) Adult riverine habitat is not limiting in the three upper Colorado River reaches for <br />razorback sucker and the recovery goal population abundance objective is below the <br />carrying capacity of the target river reaches. <br /> <br />2) The Upper Colorado River reach and the Gunnison River reach are similar with respect <br />to this carrying capacity based on similar geohydrology and predominating native fish <br />communities based on observed native/nonnative species relative abundance as described <br />in Burdick (1995) and Anderson (1997). This similarity is also assumed to extend to the <br />Palisade-Stateline reach of the Colorado River. <br /> <br />3) Successful reproduction and self-sustaining status will necessitate the presence and <br />adequate distribution and amounts of nursery habitat in flooded bottomlands or backwaters <br />maintained by a natural flow regime and favorably enhanced by nonnative fish control <br />activities. <br /> <br />7 <br />